This invention relates generally to electromagnetic door holders and more particularly to armature assemblies for use with electromagnetic door holders.
Electromagnetic door holders are commonly used to hold fire doors open in hospitals, schools, hotels, and other buildings having corridors where fire doors are present and traffic is heavy. The electromagnet is normally wired into the fire alarm system or other emergency system for the building. When a fire is detected, the fire alarm or other emergency system will cause an interruption of power to the electromagnet. This will allow every electromagnetically held door to be released and to close, thereby containing the fire.
Since electromagnetic attractive force is proportional to contact area, it is clear that anything which reduces the area of contact between the electromagnet and the armature, will rapidly reduce the magnetic holding force. This can lead to unintended closing of fire doors which condition could create a hazard during emergency situations. Alignment and parallelism between the electromagnet and the armature plate are, therefore, important to the strength of the electromagnet-armature grip.
Misalignment and out of parallelism can be caused by structural sagging, improper matching of standoff distance between the door hinges and the electromagnet assembly, and defects in workmanship during mounting of the doors, the electromagnet, and the armature plates. Regardless of the cause, the weakening effect of non-parallel contact is the same, and attempts have been made to provide for adjustability to overcome the non-parallel condition. Most of these attempts have permitted adjustment of parallelism, but have failed to provide for alignment to assure complete face to face contact between the electromagnet and the armature.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.